012 Midterm Exam Solution
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| ECE374: First Midterm 5 d. Now clients in both LANs are active and the both caches are on (similar to c. 60% of the requests can be satisfied by the local caches. What is the average rate at which each client can receive data Answer: 25Mbps link remains bottleneck link which is not shared between LANs. Answer is same as inc. Note that we assume that the 100Mbps link is shared at fine granularity, so that each client gets up to 50Mbps over that link. e. Now consider Figure 2 where the network has been extended by two additional LANs, which are connected via 25Mbps links and the throughput of the server link is only 80Mbps. In all four LANs 60% of the requests can be satisfied by the local caches. What is the average rate at which each client can receive data Answer: Now the server link is the bottleneck link an equally shared by all clients, each getting 20Mbps. 40% of the client requests are served at 20Mbps and 60% of the requests are delivered at 1Gbps, resulting in an average rate of 608Mbps. Only a reduction by 2Mbps on average despite a 50% reduction in server link bandwidth. This shows how efficient caching can be! Figure 2 Server Cache Client Cache Client 25 Mbps 200 ms Mbps 50 ms Gbps 0 ms Cache Client Cache Client |